Increased depth of field for mixed-reality display

ABSTRACT

Optical systems and methods for operation thereof are disclosed. A delimited zone is defined as a function of distance from the optical system based on a VAC limit, the delimited zone having at least one distance threshold. A virtual distance of a virtual depth plane from the optical system at which a virtual object is to be displayed is determined. It is determined whether the virtual distance is outside the delimited zone by comparing the virtual distance to the at least one distance threshold. A collimated pixel beam associated with the virtual object is generated by a projector of the optical system. The collimated pixel beam is modified to generate a modified pixel beam if the virtual distance is outside the delimited zone. Modifying the collimated pixel beam includes converging the collimated pixel beam and/or reducing a diameter of the collimated pixel beam.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/946,291, filed Dec. 10, 2019, entitled“INCREASED DEPTH OF FIELD FOR MIXED-REALITY DISPLAY,” the entire contentof which is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality” or “augmentedreality” experiences, wherein digitally reproduced images or portionsthereof are presented to a user in a manner wherein they seem to be, ormay be perceived as, real. A virtual reality, or “VR,” scenariotypically involves presentation of digital or virtual image informationwithout transparency to other actual real-world visual input; anaugmented reality, or “AR,” scenario typically involves presentation ofdigital or virtual image information as an augmentation to visualizationof the actual world around the user.

Despite the progress made in these display technologies, there is a needin the art for improved methods, systems, and devices related toaugmented reality systems, particularly, display systems.

SUMMARY OF THE INVENTION

The present disclosure relates generally to techniques for improving theperformance and user experience of optical systems. More particularly,embodiments of the present disclosure provide systems and methods foroperating a fixed focal plane optical system comprising a microdisplayand a leaky-grating light guide pupil-expanding eyepiece element with ascheme to disrupt human visual system accommodation cues by dynamicallyextending the depth of field of that system in a compact form factor.Although the present invention is described in reference to an opticalsystem such as an augmented reality (AR) device, the disclosure isapplicable to a variety of applications in computer vision and imagedisplay systems.

A summary of the invention is provided below in reference to a series ofexamples. As used below, any reference to a series of examples is to beunderstood as a reference to each of those examples disjunctively (e.g.,“Examples 1-4” is to be understood as “Examples 1, 2, 3, or 4”).

Example 1 is a method of operating an optical system, the methodcomprising: defining, based on a vergence-accommodation conflict (VAC)limit, a delimited zone as a function of distance from the opticalsystem, the delimited zone having at least one distance threshold;determining a virtual distance of a virtual depth plane from the opticalsystem at which a virtual object is to be displayed; determining whetherthe virtual distance is outside the delimited zone by comparing thevirtual distance to the at least one distance threshold; generating, bya projector of the optical system, a collimated pixel beam associatedwith the virtual object; based on determining that the virtual distanceis outside the delimited zone, modifying the collimated pixel beam togenerate a modified pixel beam, wherein modifying the collimated pixelbeam includes at least one of: converging the collimated pixel beam; orreducing a diameter of the collimated pixel beam; injecting the modifiedpixel beam into an eyepiece of the optical system; and outputting themodified pixel beam from the eyepiece toward an eye of a user.

Example 2 is an optical system comprising: a projector configured togenerate a collimated pixel beam associated with a virtual object; alight modifying device configured to modify the collimated pixel beam togenerate a modified pixel beam; an eyepiece configured to output themodified pixel beam; and a processing module configured to performoperations comprising: determining a virtual distance of a virtual depthplane from the optical system at which the virtual object is to bedisplayed; comparing the virtual distance to at least one distancethreshold; and based on comparing the virtual distance to the at leastone distance threshold, causing the light modifying device to modify thecollimated pixel beam to generate the modified pixel beam.

Example 3 is the optical system of example(s) 2, wherein modifying thecollimated pixel beam includes: converging the collimated pixel beam.

Example 4 is the optical system of example(s) 2-3, wherein modifying thecollimated pixel beam includes: reducing a diameter of the collimatedpixel beam.

Example 5 is the optical system of example(s) 2-4, wherein theoperations further comprise: defining a delimited zone as a function ofdistance from the optical system, the delimited zone including the atleast one distance threshold.

Example 6 is the optical system of example(s) 5, wherein comparing thevirtual distance to the at least one distance threshold includes:determining whether the virtual distance is outside the delimited zone.

Example 7 is the optical system of example(s) 5-6, wherein the delimitedzone is defined based on a VAC limit.

Example 8 is the optical system of example(s) 7, wherein the VAC limitis defined by a user of the optical system.

Example 9 is the optical system of example(s) 2-8, wherein the at leastone distance threshold includes an upper distance threshold.

Example 10 is the optical system of example(s) 9, wherein comparing thevirtual distance to the at least one distance threshold includes:determining whether the virtual distance is greater than the upperdistance threshold.

Example 11 is the optical system of example(s) 10, wherein modifying thecollimated pixel beam based on comparing the virtual distance to the atleast one distance threshold includes: in response to determining thatthe virtual distance is greater than the upper distance threshold,causing the light modifying device to modify the collimated pixel beam.

Example 12 is the optical system of example(s) 2-11, wherein the atleast one distance threshold includes a lower distance threshold.

Example 13 is the optical system of example(s) 12, wherein comparing thevirtual distance to the at least one distance threshold includes:determining whether the virtual distance is less than the lower distancethreshold.

Example 14 is the optical system of example(s) 13, wherein modifying thecollimated pixel beam based on comparing the virtual distance to the atleast one distance threshold includes: in response to determining thatthe virtual distance is less than the lower distance threshold, causingthe light modifying device to modify the collimated pixel beam.

Example 15 is the optical system of example(s) 2-14, wherein theeyepiece is configured to receive the modified pixel beam from the lightmodifying device.

Example 16 is the optical system of example(s) 2-15, wherein the lightmodifying device is positioned in an optical path between the projectorand the eyepiece.

Example 17 is a method of operating an optical system, the methodcomprising: determining a virtual distance of a virtual depth plane fromthe optical system at which a virtual object is to be displayed;comparing the virtual distance to at least one distance threshold;generating, by a projector of the optical system, a collimated pixelbeam associated with the virtual object; and based on comparing thevirtual distance to the at least one distance threshold, modifying thecollimated pixel beam to generate a modified pixel beam.

Example 18 is the method of example(s) 17, wherein modifying thecollimated pixel beam includes: converging the collimated pixel beam.

Example 19 is the method of example(s) 17-18, wherein modifying thecollimated pixel beam includes: reducing a diameter of the collimatedpixel beam.

Example 20 is the method of example(s) 17-19, further comprising:defining a delimited zone as a function of distance from the opticalsystem, the delimited zone including the at least one distancethreshold.

Example 21 is the method of example(s) 20, wherein comparing the virtualdistance to the at least one distance threshold includes: determiningwhether the virtual distance is outside the delimited zone.

Example 22 is the method of example(s) 20-21, wherein the delimited zoneis defined based on a VAC limit.

Example 23 is the method of example(s) 22, wherein the VAC limit isdefined by a user of the optical system.

Example 24 is the method of example(s) 17-23, wherein the at least onedistance threshold includes an upper distance threshold.

Example 25 is the method of example(s) 24, wherein comparing the virtualdistance to the at least one distance threshold includes: determiningwhether the virtual distance is greater than the upper distancethreshold.

Example 26 is the method of example(s) 25, wherein modifying thecollimated pixel beam based on comparing the virtual distance to the atleast one distance threshold includes: in response to determining thatthe virtual distance is greater than the upper distance threshold,modifying the collimated pixel beam.

Example 27 is the method of example(s) 17-26, wherein the at least onedistance threshold includes a lower distance threshold.

Example 28 is the method of example(s) 27, wherein comparing the virtualdistance to the at least one distance threshold includes: determiningwhether the virtual distance is less than the lower distance threshold.

Example 29 is the method of example(s) 28, wherein modifying thecollimated pixel beam based on comparing the virtual distance to the atleast one distance threshold includes: in response to determining thatthe virtual distance is less than the lower distance threshold,modifying the collimated pixel beam.

Example 30 is the method of example(s) 17-29, further comprising:injecting the modified pixel beam into an eyepiece of the opticalsystem.

Example 31 is the method of example(s) 17-30, further comprising:outputting the modified pixel beam from an eyepiece of the opticalsystem toward an eye of a user.

Example 32 is the method of example(s) 17-31, wherein the collimatedpixel beam is modified by a light modifying device positioned in anoptical path between the projector and an eyepiece of the opticalsystem.

Numerous benefits are achieved by way of the present disclosure overconventional techniques. For example, embodiments enable a single focalplane system to have several of the same benefits as a two-focal planesystem, such as reduced VAC in both the near-field and far-field virtualdepth planes. Additionally, since the pixel beam can be modified priorto injection into the eyepiece, embodiments are compatible with existingeyepieces that employ pupil-expansion combiner eyepiece technology.Embodiments also eliminate the need for clipping planes that are oftenemployed for near field depth planes, thereby reducing the inconvenienceto users due to virtual content disappearing. Other benefits of thepresent disclosure will be readily apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure, are incorporated in and constitute apart of this specification, illustrate embodiments of the disclosure andtogether with the detailed description serve to explain the principlesof the disclosure. No attempt is made to show structural details of thedisclosure in more detail than may be necessary for a fundamentalunderstanding of the disclosure and various ways in which it may bepracticed.

FIG. 1 illustrates an augmented reality (AR) scene as viewed through awearable AR device.

FIG. 2A illustrates an AR device having a single fixed focal plane.

FIG. 2B illustrates an AR device having two fixed focal planes.

FIG. 3 illustrates the relationship between vergence-accommodationconflict (VAC) and the distance of the virtual depth plane.

FIG. 4 illustrates a schematic view of an example wearable AR device.

FIG. 5 illustrates an example function of a viewing optics assembly ofan AR device and the resulting user visual percept of the system'soutput.

FIG. 6 illustrates an example function of a viewing optics assembly ofan AR device and the resulting user visual percept of the system'soutput.

FIG. 7 illustrates an example function of a viewing optics assembly ofan AR device and the resulting user visual percept of the system'soutput.

FIG. 8 illustrates an example function of a viewing optics assembly ofan AR device and the resulting user visual percept of the system'soutput.

FIG. 9 illustrates an example function of a viewing optics assembly ofan AR device and the resulting user visual percept of the system'soutput.

FIGS. 10A-10C illustrate an example light modifying device for reducingthe diameter of the collimated pixel beam.

FIG. 11 illustrates an example control scheme for a light modifyingdevice and the corresponding user visual percept of the system's output.

FIG. 12 illustrates an example method for defining a VAC delimited zone.

FIG. 13 illustrates various examples of VAC delimited zones.

FIG. 14 illustrates an example method of operating an optical system.

FIG. 15 illustrates a simplified computer system.

In the appended figures, similar components and/or features may have thesame numerical reference label. Further, various components of the sametype may be distinguished by following the reference label with a letteror by following the reference label with a dash followed by a secondnumerical reference label that distinguishes among the similarcomponents and/or features. If only the first numerical reference labelis used in the specification, the description is applicable to any oneof the similar components and/or features having the same firstnumerical reference label, irrespective of the suffix.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Mixed-reality (MR) and augmented reality (AR) wearable displays arecapable of presenting virtual content to a user over a wide depth range.For many displays, a user may experience varying levels ofaccommodation-vergence conflict (VAC) at different depths, which occurswhen the user's brain receives mismatching cues between the distance ofa virtual object from the user's eyes and the focusing distance requiredfor the eyes to focus on that virtual object. VAC leads to visualfatigue, headache, nausea, and eyestrain, and remains a significantsource of discomfort for users. Accordingly, to maintain user comfort,modern MR and AR wearable displays may consider a VAC budget allowancewhen delivering virtual content over a depth range, which may result ina depth range that is significantly reduced.

Various approaches to mitigate VAC have been implemented. One approachincludes adding a second depth plane and a vari-focal switch based oneye-tracking to the optical system. Another approach is to add avari-focal element with the ability to sweep eyepiece focal planesacross a broad range. These approaches come with increased volume in theform of additional eyepiece layers and/or through integration ofliquid-Tillable tunable lens pairs straddling the eyepiece, as well asincreased complexity due to complex illumination schemes.

Some embodiments of the present invention provide an optical system witha delimited zone, within which a limited amount of VAC is tolerated by auser, and outside of which an expanded depth of field can be switched onto disrupt human visual system accommodation cues. In some embodiments,the delimited zone can be defined based on a single or multiple fixedfocal plane(s) or a single or multiple variable focus plane(s). Virtualcontent having an associated virtual depth plane that lies within thedelimited zone may be projected to the user in a normal manner, whereasvirtual content outside the delimited zone is modified by a lightmodifying device so as to reduce the reliability of the accommodationcues.

In some instances, the light modifying device may cause the collimatedlight generated by a projector to become converging when entering theeyepiece. This causes the virtual image light (i.e., light associatedwith a virtual image) that is outcoupled from the leaky-grating of theeyepiece to also be converging. However, the chief ray of each beamletdoes not change direction, resulting in a virtual image with vergencecues but very weak accommodation cues. Such a virtual image can disruptthe vergence-accommodation response in areas of the depth of field whereVAC would exceed the threshold tolerance. Thus, embodiments disclosedherein can extend the depth of field of the optical system, since theuser's eye may not be able to focus on pixels at the virtual depthplane. Additionally or alternatively, the light modifying device mayreduce the diameter of each collimated pixel beam generated by theprojector. This can cause the light that is outcoupled from theleaky-grating of the eyepiece to likewise have pixel beams with reduceddiameters, thereby disrupting the accommodation cues associated with theoutcoupled light.

In some instances, optical see-through (OST) AR devices can improvevirtual content being presented to a user by applying optical power tothe virtual image light using one or more lens assemblies arrangedwithin an optical stack. Embodiments of the present invention arecompatible with existing systems that utilize lens assemblies to varythe virtual depth plane of the virtual object.

FIG. 1 illustrates an AR scene 100 as viewed through a wearable ARdevice, according to some embodiments. AR scene 100 is depicted whereina user of an AR technology sees a real-world park-like setting 106featuring various real-world objects 130 such as people, trees,buildings in the background, and a real-world concrete platform 120. Inaddition to these items, the user of the AR technology also perceivesthat they “see” various virtual objects 102 such as a robot statue 102-2standing upon the real-world concrete platform 120, and a cartoon-likeavatar character 102-1 flying by, which seems to be a personification ofa bumble bee, even though these elements (character 102-1 and statue102-2) do not exist in the real world. Due to the extreme complexity ofthe human visual perception and nervous system, it is challenging toproduce a virtual reality (VR) or AR technology that facilitates acomfortable, natural-feeling, rich presentation of virtual imageelements amongst other virtual or real-world imagery elements.

FIG. 2A illustrates an AR device 200A having a single fixed focal plane,according to some embodiments. During operation, a projector 214 of ARdevice 200A may project virtual image light 223 (i.e., light associatedwith virtual content) onto an eyepiece 202-1, which may cause a lightfield (i.e., an angular representation of virtual content) to beprojected onto a retina of a user in a manner such that the userperceives the corresponding virtual content as being positioned at somelocation within the user's environment. For example, virtual image light223 outcoupled by eyepiece 202-1 may cause the user to perceivecharacter 102-1 as being positioned at a first virtual depth plane 210-1and statue 102-2 as being positioned at a second virtual depth plane210-2. The user perceives the virtual content along with world light 232corresponding to one or more world objects 230, such as platform 120.

In some embodiments, AR device 200A includes a first lens assembly 205-1positioned on the user side of eyepiece 202-1 (the side of eyepiece202-1 closest to the eye of the user) and a second lens assembly 205-2positioned on the world side of eyepiece 202-1. Each of lens assemblies205-1, 205-2 may be configured to apply optical power to the lightpassing therethrough.

FIG. 2B illustrates an AR device 200B having two fixed focal planes,according to some embodiments. During operation, projector 214 mayproject virtual image light 223 onto first eyepiece 202-1 and a secondeyepiece 202-2, which may cause a light field to be projected onto aretina of a user in a manner such that the user perceives thecorresponding virtual content as being positioned at some locationwithin an environment of the user. For example, virtual image light 223outcoupled by first eyepiece 202-1 may cause the user to perceivecharacter 102-1 as being positioned at a first virtual depth plane 210-1and virtual image light 223 outcoupled by second eyepiece 202-2 maycause the user to perceive statue 102-2 as being positioned at a secondvirtual depth plane 210-2.

FIG. 3 illustrates the relationship between VAC and the distance of thevirtual depth plane for each of AR devices 200A, 200B described inreference to FIGS. 2A and 2B, respectively. For AR device 200B, thetwo-focal plane system provides switchable focal planes at 1.95 diopters(0.51 meters) and 0.65 diopters (1.54 meters), with a switch point at1.3 diopters (0.77 meters), a near content limit (clipping plane) at 2.7diopters (0.37 meters), and an ability to provide imagery neverexceeding 1.0 diopter VAC between that plane and infinity. For AR device200A, the single fixed focal plane system has a focal plane location at1.5 diopters (0.6 meters) and a near content limit of 2.5 diopters (0.4meters) and a far content limit of 0.31 diopters (3.2 meters), assuminga maximum allowable VAC of 1.0 diopter. Such a configuration would havea usable range of 0.4-3.2 meters with content falling outside of thatrange requiring some solution to mitigate exceeding the VAC limit.

FIG. 4 illustrates a schematic view of an example wearable AR device400, according to some embodiments of the present invention. AR device400 may include a left eyepiece 402A and a left lens assembly 405Aarranged in a side-by-side configuration and a right eyepiece 402B and aright lens assembly 405B also arranged in a side-by-side configuration.In some embodiments, AR device 400 includes one or more sensorsincluding, but not limited to: a left front-facing world camera 406Aattached directly to or near left eyepiece 402A, a right front-facingworld camera 406B attached directly to or near right eyepiece 402B, aleft side-facing world camera 406C attached directly to or near lefteyepiece 402A, and a right side-facing world camera 406D attacheddirectly to or near right eyepiece 402B. In some embodiments, AR device400 includes one or more image projection devices such as a leftprojector 414A optically linked to left eyepiece 402A and a rightprojector 414B optically linked to right eyepiece 402B.

Some or all of the components of AR device 400 may be head mounted suchthat projected images may be viewed by a user. In one particularimplementation, all of the components of AR device 400 shown in FIG. 4are mounted onto a single device (e.g., a single headset) wearable by auser. In another implementation, one or more components of a processingmodule 450 are physically separate from and communicatively coupled tothe other components of AR device 400 by one or more wired and/orwireless connections. For example, processing module 450 may include alocal module 452 on the head mounted portion of AR device 400 and aremote module 456 physically separate from and communicatively linked tolocal module 452. Remote module 456 may be mounted in a variety ofconfigurations, such as fixedly attached to a frame, fixedly attached toa helmet or hat worn by a user, embedded in headphones, or otherwiseremovably attached to a user (e.g., in a backpack-style configuration,in a belt-coupling style configuration, etc.).

Processing module 450 may include a processor and an associated digitalmemory, such as non-volatile memory (e.g., flash memory), both of whichmay be utilized to assist in the processing, caching, and storage ofdata. The data may include data captured from sensors (which may be,e.g., operatively coupled to AR device 400) or otherwise attached to auser, such as cameras 406, an ambient light sensor, eye trackers,microphones, inertial measurement units, accelerometers, compasses, GPSunits, radio devices, and/or gyros. For example, processing module 450may receive image(s) 420 from cameras 406. Specifically, processingmodule 450 may receive left front image(s) 420A from left front-facingworld camera 406A, right front image(s) 420B from right front-facingworld camera 406B, left side image(s) 420C from left side-facing worldcamera 406C, and right side image(s) 420D from right side-facing worldcamera 406D. In some embodiments, image(s) 420 may include a singleimage, a pair of images, a video comprising a stream of images, a videocomprising a stream of paired images, and the like. Image(s) 420 may beperiodically generated and sent to processing module 450 while AR device400 is powered on, or may be generated in response to an instructionsent by processing module 450 to one or more of the cameras. As anotherexample, processing module 450 may receive ambient light informationfrom an ambient light sensor. As another example, processing module 450may receive gaze information from one or more eye trackers. As anotherexample, processing module 450 may receive image information (e.g.,image brightness values) from one or both of projectors 414.

Cameras 406A, 406B may be positioned to capture images thatsubstantially overlap within the field of view of a user's left andright eyes, respectively. Accordingly, placement of cameras 406 may benear a user's eyes but not so near as to obscure the user's field ofview. Alternatively or additionally, cameras 406A, 406B may bepositioned so as to align with the incoupling locations of virtual imagelight 422A, 422B, respectively. Cameras 406C, 406D may be positioned tocapture images to the side of a user, e.g., in a user's peripheralvision or outside the user's peripheral vision. Image(s) 420C, 420Dcaptured using cameras 406C, 406D need not necessarily overlap withimage(s) 420A, 420B captured using cameras 406A, 406B.

Eyepieces 402A, 402B may comprise transparent or semi-transparentwaveguides configured to direct and outcouple light generated byprojectors 414A, 414B, respectively. Specifically, processing module 450may cause left projector 414A to output left virtual image light 422Aonto left eyepiece 402A, and may cause right projector 414B to outputright virtual image light 422B onto right eyepiece 402B. In someembodiments, each of eyepieces 402A, 402B may comprise a plurality ofwaveguides corresponding to different colors. In some embodiments, lensassemblies 405A, 405B may be coupled to and/or integrated with eyepieces402A, 402B. For example, lens assemblies 405A, 405B may be incorporatedinto a multi-layer eyepiece and may form one or more layers that make upone of eyepieces 402A, 402B.

In some embodiments, AR device 400 includes one or more light modifyingdevices 404A, 404B for modifying virtual image light 422A, 422B.Specifically, a left light modifying device 404A may be positioned in anoptical path between left projector 414A and left eyepiece 402A so as tomodify left virtual image light 422A prior to being outputted onto lefteyepiece 402A, and a right light modifying device 404B may be positionedin an optical path between right projector 414B and right eyepiece 402Bso as to modify right virtual image light 422B prior to being outputtedonto right eyepiece 402B. In some embodiments, light modifying devices404A, 404B may be integrated with projectors 414A, 414B. In someembodiments, light modifying devices 404A, 404B may be integrated witheyepieces 402A, 402B.

In some embodiments, projectors 414A, 414B may include amicro-electromechical system (MEMS) spatial light modulator (SLM)scanning device. In such embodiments, light modifying devices 404A, 404Bmay employ a varifocal mirror or lens that can be used in the laserbeams prior to the scanning mirrors. If a relay optical system is used,one of the optical elements within the relay optics could be vari-focaland be switched to provide converging pixel rays to the ICG formed onthe eyepieces. If a standard projection system is used with apixel-based SLM (such as a liquid crystal on silicon (LCOS)), the SLMitself could be translated in the z-axis (perpendicular to the array),such that the projection lens produces a finite external focal plane(and thus convergent pixel rays). In some embodiments, a vari-focal lenscould be incorporated between the projection/relay lens of themicrodisplay and the ICG of the eyepiece itself, converting the outputcollimated pixel rays into convergent states.

FIG. 5 illustrates an example function of a viewing optics assembly 500of an AR device and the resulting user visual percept of the system'soutput. Viewing optics assembly 500 includes a projector 514 and aneyepiece 502. Projector 514 generates a collimated pixel beam 516 thatis carried onto an eyepiece 502 at an input coupling grating (ICG) 503formed on eyepiece 502. After being diffracted by ICG 503, collimatedpixel beam 516 propagates in eyepiece 502 until an output grating formedon eyepiece 502 diffracts the light toward the user.

A leaky-grating light-guide, pupil-expanding eyepiece with no programmedoptical power produces a virtual image at infinity. The percept isproduced by multiple output “beamlets” (emitted replicants of the inputpixel wavefronts) collected through the pupil and imaged onto the retinaof the user's eye. In this case, when the user's eye is focused atinfinity, a sharp image of the pixel is formed on the retina. When theeye is focused at another plane (for example at 1.33 meters from theuser) a blurry image of the pixel is formed on the retina.

FIG. 6 illustrates an example function of a viewing optics assembly 600of an AR device and the resulting user visual percept of the system'soutput. Viewing optics assembly 600 includes a projector 614 thatgenerates a collimated pixel beam 616 that is carried onto an eyepiece602 at an ICG 603 formed on eyepiece 602. After being diffracted by ICG603, collimated pixel beam 616 propagates in eyepiece 602 until anoutput grating formed on eyepiece 602 diffracts the light toward theuser.

Viewing optics assembly 600 includes a −0.75 diopters lens assembly 605that modulates the wavefronts of the emitted beamlets, diverging themwith respect to each other and diverging each ray independently, so asto both focus pixel light and converge beamlets at 1.33 meters from theuser's eye. Lens assembly 605 shifts the chief rays of the emergingbeamlets and diverges the collimated output to a single pixel focusposition at the focal length of the lens. In this case, when the user'seye is focused at 1.33 meters, a sharp image of the pixel is formed onthe retina. When the eye focuses at infinity, that image is blurred.

In the example illustrated in FIG. 6 , the depth of focus of the imageis determined by several factors, including the beamlet packing density(determined by the beam diameter, the eyepiece substrate thickness,along with several other factors), the size of the user's pupil, theoptical quality of the lens assembly 605, and the inherent depth offield of the user's eye. Each of these factors may be considered todetermine an acceptable VAC budget figure for the system. In someembodiments, 1.0 diopters can be used as the VAC budget figure, althoughthis value can be higher or lower in practice.

FIG. 7 illustrates an example function of a viewing optics assembly 700of an AR device and the resulting user visual percept of the system'soutput. Viewing optics assembly 700 includes a projector 714 thatgenerates a collimated pixel beam 716 that is modified by a lightmodifying device 704 to produce a modified pixel beam 752 having aconverging wavefront. Modified pixel beam 752 is carried onto aneyepiece 702 at an ICG 703 formed on eyepiece 702. After beingdiffracted by ICG 703, modified pixel beam 752 propagates in eyepiece702 until an output grating formed on eyepiece 702 diffracts the lighttoward the user.

In the example illustrated in FIG. 7 , modifying the wavefronts of theimaged pixels introduces optical power to the projection system,transforming an infinity-focused system into a system that produces afinite image position in front of the projector. In such aconfiguration, a single pixel produces a converging (curved) wavefrontat the pupil plane of the projector. When a converging pixel ray entersthe eyepiece, the exiting beamlets maintain this convergence, however,the chief ray of each beamlet does not change direction. In this case,when the user's eye is focused either at 1.33 meters or at infinity, ablurred image of the pixel is formed on the retina. Additionally, theperceived pixel when the user's eye is focused at 1.33 meters may bedifferent from the perceived pixel when the user's eye is focused atinfinity, as depicted by different types of blur in FIG. 7 .

FIG. 8 illustrates an example function of a viewing optics assembly 800of an AR device and the resulting user visual percept of the system'soutput. Viewing optics assembly 800 includes a projector 814 thatgenerates a collimated pixel beam 816 that is modified by a lightmodifying device 804 to produce a modified pixel beam 852 having aconverging wavefront. Modified pixel beam 852 is carried onto aneyepiece 802 at an ICG 803 formed on eyepiece 802. After beingdiffracted by ICG 803, modified pixel beam 852 propagates in eyepiece802 until an output grating formed on eyepiece 802 diffracts the lighttoward the user. Viewing optics assembly 800 further includes a −0.75diopters lens assembly 805 positioned between eyepiece 802 and theuser's eye that modulates the wavefronts of the emitted beamlets.

In the example illustrated in FIG. 8 , lens assembly 805 collimates eachbeamlet output while simultaneously re-directing the chief ray of eachbeamlet to pivot around a point at the focal plane of the lens. As aresult, when the user's eye is focused at 1.33 meters, a blurred imageof the pixel is formed on the retina. When the user's eye is focused atinfinity, a percept comprising a repeated structure of blurred images isproduced. The user's eye is unable to bring the blurred image intofocus, thereby disrupting the user's physiologicalvergence-accommodation cues and reducing the uncomfortable effects ofvergence-accommodation conflict. This percept having a repeatedstructure allows virtual content to exist on planes outside of the VACthreshold. As a result, the depth of field of the optical system canextend beyond the VAC threshold without discomfort, since the user's eyewill not be able to focus on pixels at the virtual depth plane.

FIG. 9 illustrates an example function of a viewing optics assembly 900of an AR device and the resulting user visual percept of the system'soutput. Viewing optics assembly 900 includes a projector 914 thatgenerates a collimated pixel beam 916 that is modified by a lightmodifying device 904 such as a spatial light modulator (SLM), relayoptics, polarizers, beam splitters, lenses or a combination thereof, toproduce a modified pixel beam 952 having a reduced diameter. Modifiedpixel beam 952 is carried onto an eyepiece 902 at an ICG 903 formed oneyepiece 902. After being diffracted by ICG 903, modified pixel beam 952propagates in eyepiece 902 until an output grating formed on eyepiece902 diffracts the light toward the user. Viewing optics assembly 900further includes lens assemblies 905 including a −1 diopter componentpositioned between eyepiece 902 and the user's eye and a +1 dioptercomponent positioned on the world side of eyepiece 902.

In the example illustrated in FIG. 9 , vergence-accommodation cues aredisrupted and the depth of field of the system is extended by modulatingthe diameter of the laser beam, rather than throughdivergence/convergence of the image light. This may be performed bylight modifying device 904 prior to injecting the light into ICG 903. Inthis case, the percept is driven by the inability of the lens assemblybetween eyepiece 902 and the user's eye to provide a small focal spotdue to the reduced size of the pixel beam.

FIGS. 10A-10C illustrate an example light modifying device for reducingthe diameter of the collimated pixel beam, according to some embodimentsof the present invention. By varying the position of a second lens 1004relative to a first lens 1002 and a third lens 1006, the diameter of theinput collimated pixel beam can be expanded, reduced, or leftunmodified. In reference to FIG. 10A, second lens 1004 is adjusted to bepositioned closer to first lens 1002 than to third lens 1006 (e.g.,adjacent to first lens 1002), causing the diameter of the collimatedpixel beam to become expanded upon exiting the light modifying device.In reference to FIG. 10B, second lens 1004 is adjusted to be positionedat a midpoint between first lens 1002 and third lens 1006, causing thediameter of the collimated pixel beam to be left unmodified upon exitingthe light modifying device. In reference to FIG. 10C, second lens 1004is adjusted to be positioned closer to third lens 1006 than to firstlens 1002 (e.g., adjacent to third lens 1006), causing the diameter ofthe collimated pixel beam to become reduced upon exiting the lightmodifying device.

In some embodiments, the light modifying device illustrated in FIGS.10A-10C is used to dynamically change the diameter of a MEMS laser beam.In some instances, the light modifying device may be positioned prior tothe MEMS mirror(s) so as to modify the laser beam prior to entering theMEMS mirror(s).

FIG. 11 illustrates an example control scheme for a light modifyingdevice and the corresponding user visual percept of the system's output,according to some embodiments of the present invention. In someembodiments, a VAC delimited zone 1102 is defined based on a desired VAClimit, such as 1 diopter. VAC delimited zone 1102 may include a lowerdistance threshold 1104, below which the VAC experienced by a userexceeds the VAC limit, and an upper distance threshold 1106, above whichthe VAC experienced by a user exceeds the VAC limit.

Under the control scheme, when it is determined that the distance of thevirtual depth plane (from the AR device or user) is less than lowerdistance threshold 1104, the light modifying device is caused to modifythe wavefront of the collimated pixel beam. When it is determined thatthe distance of the virtual depth plane is greater than lower distancethreshold 1104 and less than upper distance threshold 1106 (i.e., iswithin VAC delimited zone 1102), the light modifying device is caused tonot modify the collimated pixel beam and to output the collimated pixelbeam without modification. When it is determined that the distance ofthe virtual depth plane is greater than upper distance threshold 1106,the light modifying device is caused to modify the wavefront of thecollimated pixel beam.

The control scheme may optionally implement gradual modifications to thecollimated pixel beam at or near the distance thresholds. For example,the light modifying device may impart partial modifications to thecollimated pixel beam for virtual distances just before a distancethreshold, greater modifications at the distance threshold, and fullmodifications well past the distance threshold. As one example, for anupper distance threshold of 3.2 meters, a control scheme may beimplemented in which the collimated pixel beam is converged at 0% for avirtual distance of 2.8 meters, 25% for a virtual distance of 3.0meters, 50% for a virtual distance of 3.2 meters, 75% for a virtualdistance of 3.4 meters, and 100% for a virtual distance of 3.6 meters.In the same or a different example, for a lower distance threshold of0.4 meters, a control scheme may be implemented in which the collimatedpixel beam is converged at 0% for a virtual distance of 0.6 meters, 25%for a virtual distance of 0.5 meters, 50% for a virtual distance of 0.4meters, 75% for a virtual distance of 0.3 meters, and 100% for a virtualdistance of 0.2 meters. Control schemes with longer or shortertransition bands than the above examples may be implemented. One ofordinary skill in the art will see various variations, alternatives, andmodifications.

FIG. 12 illustrates an example method for defining a VAC delimited zone1202, according to some embodiments of the present invention. First, theVAC experienced by a user is plotted as a function of the distance ofthe virtual depth plane from the AR device (alternatively referred to asthe “VAC plot”). In some embodiments, the VAC plot is determined basedon the focal plane design of the AR device. For the VAC plot illustratedin FIG. 12 , a 0.75 meters focal plane is utilized. Next, the VAC limitis plotted alongside the VAC experienced by the user. Next, intersectionpoints 1204, 1206 between the two plots are identified and thecorresponding distances are used as lower and upper distance thresholdsof VAC zone 1202, respectively.

FIG. 13 illustrates various examples of VAC delimited zones that may bedefined based on VAC plots for various single focal plane systems. Asthe focal plane of the AR device increases, both the lower distancethreshold and the upper distance threshold of the VAC delimited zoneincrease, presenting a trade-off between near-field versus far-fieldperformance. Additional depth planes can be added to the system toincrease the VAC delimited zone.

FIG. 14 illustrates an example method 1400 of operating an opticalsystem (e.g., AR device 400), according to some embodiments of thepresent invention. One or more steps of method 1400 may be performed ina different order than the illustrated embodiment, and one or more stepsof method 1400 may be omitted during performance of method 1400.Furthermore, two or more steps of method 1400 may be performedsimultaneously or concurrently with each other.

At step 1402, a VAC delimited zone (e.g., VAC delimited zones 1102,1202) is defined. In some embodiments, the VAC delimited zone is definedbased on the number of focal planes of the optical device and/or theircorresponding focal plane locations. For example, the VAC associatedwith a single focal plane system with a focal plane location at 1.5diopters can be estimated and used to determine the VAC delimited zone,which may be significantly smaller than the VAC delimited zonedetermined using the VAC associated with a multiple focal plane system,such as, for example, a two-focal plane system with focal planelocations at 1.95 diopters and 0.65 diopters. In some embodiments, theVAC delimited zone is additionally (or alternatively) defined based on aVAC limit, which may be specified by a user or may be predetermined forthe system. In some embodiments, the VAC delimited zone is defined byfinding the intersection point(s) (e.g., intersection points 1204, 1206)between the VAC associated with the optical system and the VAC limit, asdescribed at least in reference to FIGS. 3, 12, and 13 .

In some embodiments, the VAC delimited zone is defined as a function ofdistance from the optical system, where distances inside the VACdelimited zone correspond to virtual depth planes at which virtualcontent causes a user to experience VAC less than the VAC limit, anddistances outside the VAC delimited zone correspond to virtual depthplanes at which virtual content causes a user to experience VAC greaterthan the VAC limit. In some embodiments, the VAC delimited zone includesat least one distance threshold. For example, the VAC delimited zone mayinclude a lower distance threshold (e.g., lower distance threshold 1104)and/or an upper distance threshold (e.g., upper distance threshold1106), the lower distance threshold being less than the upper distancethreshold.

At step 1404, a virtual distance of a virtual depth plane (e.g., virtualdepth planes 210) from the optical system at which a virtual object(e.g., virtual objects 102) is to be displayed is determined. Thevirtual distance may be expressed in meters, diopters, or some otherunit that indicates physical displacement. In some embodiments, thevirtual distance is determined by a processing module (e.g., processingmodule 450). In some embodiments, the virtual distance is determinedprior to, during, or after the collimated pixel beam associated with thevirtual object is generated by the optical system.

At step 1406, the virtual distance is compared to the lower distancethreshold and/or the upper distance threshold. In some embodiments, itis determined whether the virtual distance is less than the lowerdistance threshold, greater than the lower distance threshold and lessthan the upper distance threshold, or greater than the upper distancethreshold. For example, in some embodiments, step 1406 may includedetermining whether the virtual distance is less than the lower distancethreshold. As another example, in some embodiments, step 1406 mayinclude determining whether the virtual distance is greater than theupper distance threshold. As another example, in some embodiments, step1406 may include determining whether the virtual distance is less thanthe lower distance threshold or greater than the upper distancethreshold. In some embodiments, step 1406 is equivalent to determiningwhether the virtual distance is outside the VAC delimited zone.

At step 1408, a collimated pixel beam (e.g., collimated pixel beams 516,616, 716, 816, 916) associated with the virtual object is generated bythe optical system. In some embodiments, the collimated pixel beam isgenerated by a projector (e.g., projectors 214, 414, 514, 614, 714, 814,914) of the optical system. The collimated pixel beam may contain color,brightness, and size information for displaying the virtual object. Forexample, the collimated pixel beam may include light from a single LEDcolor source (e.g., red) or from multiple LED color sources (e.g., red,green, and blue).

At step 1410, the collimated pixel beam is modified to generate amodified pixel beam (e.g., modified pixel beams 752, 852, 952). In someembodiments, the collimated pixel beam is modified by a light modifyingdevice (e.g., light modifying devices 404, 704, 804, 904) of the opticalsystem. In some embodiments, whether or not step 1410 is performed maydepend on the comparison performed in step 1406. For example, in someembodiments, step 1410 is performed only when it is determined that thevirtual distance is outside the VAC delimited zone. For example, step1410 may only be performed in response to determining that the virtualdistance is less than the lower distance threshold or in response todetermining that the virtual distance is greater than the upper distancethreshold. In some embodiments, the light modifying device is integratedwith the projector. In some embodiments, the light modifying device isseparate from the projector.

In some embodiments, step 1410 includes step 1412 and/or step 1414. Atstep 1412, the collimated pixel beam is converged. In some embodiments,the collimated pixel beam is converged by the light modifying device. Atstep 1414, a diameter of the collimated pixel beam is reduced. In someembodiments, the diameter of the collimated pixel beam is reduced by thelight modifying device.

At step 1416, the modified pixel beam is injected into an eyepiece(e.g., eyepieces 202, 402, 502, 602, 702, 802, 902) of the opticalsystem. In some embodiments, the modified pixel beam is injected into anICG (e.g., ICGs 503, 603, 703, 803, 903) formed on the eyepiece.

At step 1418, the modified pixel beam is outputted from the eyepiece ofthe optical system. In some embodiments, the modified pixel beam isoutputted from a leaky-grating formed on the eyepiece. In someembodiments, the modified pixel beam is outputted from the eyepiecetoward a user's eye.

FIG. 15 illustrates a simplified computer system 1500 according to anembodiment described herein. Computer system 1500 as illustrated in FIG.15 may be incorporated into devices described herein. FIG. 15 provides aschematic illustration of one embodiment of computer system 1500 thatcan perform some or all of the steps of the methods provided by variousembodiments. It should be noted that FIG. 15 is meant only to provide ageneralized illustration of various components, any or all of which maybe utilized as appropriate. FIG. 15 , therefore, broadly illustrates howindividual system elements may be implemented in a relatively separatedor relatively more integrated manner.

Computer system 1500 is shown comprising hardware elements that can beelectrically coupled via a bus 1505, or may otherwise be incommunication, as appropriate. The hardware elements may include one ormore processors 1510, including without limitation one or moregeneral-purpose processors and/or one or more special-purpose processorssuch as digital signal processing chips, graphics accelerationprocessors, and/or the like; one or more input devices 1515, which caninclude without limitation a mouse, a keyboard, a camera, and/or thelike; and one or more output devices 1520, which can include withoutlimitation a display device, a printer, and/or the like.

Computer system 1500 may further include and/or be in communication withone or more non-transitory storage devices 1525, which can comprise,without limitation, local and/or network accessible storage, and/or caninclude, without limitation, a disk drive, a drive array, an opticalstorage device, a solid-state storage device, such as a random accessmemory (“RAM”), and/or a read-only memory (“ROM”), which can beprogrammable, flash-updateable, and/or the like. Such storage devicesmay be configured to implement any appropriate data stores, includingwithout limitation, various file systems, database structures, and/orthe like.

Computer system 1500 might also include a communications subsystem 1519,which can include without limitation a modem, a network card (wirelessor wired), an infrared communication device, a wireless communicationdevice, and/or a chipset such as a Bluetooth™ device, an 802.11 device,a WiFi device, a WiMax device, cellular communication facilities, etc.,and/or the like. The communications subsystem 1519 may include one ormore input and/or output communication interfaces to permit data to beexchanged with a network such as the network described below to name oneexample, other computer systems, television, and/or any other devicesdescribed herein. Depending on the desired functionality and/or otherimplementation concerns, a portable electronic device or similar devicemay communicate image and/or other information via the communicationssubsystem 1519. In other embodiments, a portable electronic device, e.g.the first electronic device, may be incorporated into computer system1500, e.g., an electronic device as an input device 1515. In someembodiments, computer system 1500 will further comprise a working memory1535, which can include a RAM or ROM device, as described above.

Computer system 1500 also can include software elements, shown as beingcurrently located within the working memory 1535, including an operatingsystem 1540, device drivers, executable libraries, and/or other code,such as one or more application programs 1545, which may comprisecomputer programs provided by various embodiments, and/or may bedesigned to implement methods, and/or configure systems, provided byother embodiments, as described herein. Merely by way of example, one ormore procedures described with respect to the methods discussed above,might be implemented as code and/or instructions executable by acomputer and/or a processor within a computer; in an aspect, then, suchcode and/or instructions can be used to configure and/or adapt a generalpurpose computer or other device to perform one or more operations inaccordance with the described methods.

A set of these instructions and/or code may be stored on anon-transitory computer-readable storage medium, such as the storagedevice(s) 1525 described above. In some cases, the storage medium mightbe incorporated within a computer system, such as computer system 1500.In other embodiments, the storage medium might be separate from acomputer system e.g., a removable medium, such as a compact disc, and/orprovided in an installation package, such that the storage medium can beused to program, configure, and/or adapt a general purpose computer withthe instructions/code stored thereon. These instructions might take theform of executable code, which is executable by computer system 1500and/or might take the form of source and/or installable code, which,upon compilation and/or installation on computer system 1500 e.g., usingany of a variety of generally available compilers, installationprograms, compression/decompression utilities, etc., then takes the formof executable code.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized hardware might also be used, and/or particularelements might be implemented in hardware, software including portablesoftware, such as applets, etc., or both. Further, connection to othercomputing devices such as network input/output devices may be employed.

As mentioned above, in one aspect, some embodiments may employ acomputer system such as computer system 1500 to perform methods inaccordance with various embodiments of the technology. According to aset of embodiments, some or all of the procedures of such methods areperformed by computer system 1500 in response to processor 1510executing one or more sequences of one or more instructions, which mightbe incorporated into the operating system 1540 and/or other code, suchas an application program 1545, contained in the working memory 1535.Such instructions may be read into the working memory 1535 from anothercomputer-readable medium, such as one or more of the storage device(s)1525. Merely by way of example, execution of the sequences ofinstructions contained in the working memory 1535 might cause theprocessor(s) 1510 to perform one or more procedures of the methodsdescribed herein. Additionally or alternatively, portions of the methodsdescribed herein may be executed through specialized hardware.

The terms “machine-readable medium” and “computer-readable medium,” asused herein, refer to any medium that participates in providing datathat causes a machine to operate in a specific fashion. In an embodimentimplemented using computer system 1500, various computer-readable mediamight be involved in providing instructions/code to processor(s) 1510for execution and/or might be used to store and/or carry suchinstructions/code. In many implementations, a computer-readable mediumis a physical and/or tangible storage medium. Such a medium may take theform of a non-volatile media or volatile media. Non-volatile mediainclude, for example, optical and/or magnetic disks, such as the storagedevice(s) 1525. Volatile media include, without limitation, dynamicmemory, such as the working memory 1535.

Common forms of physical and/or tangible computer-readable mediainclude, for example, a floppy disk, a flexible disk, hard disk,magnetic tape, or any other magnetic medium, a CD-ROM, any other opticalmedium, punchcards, papertape, any other physical medium with patternsof holes, a RAM, a PROM, EPROM, a FLASH-EPROM, any other memory chip orcartridge, or any other medium from which a computer can readinstructions and/or code.

Various forms of computer-readable media may be involved in carrying oneor more sequences of one or more instructions to the processor(s) 1510for execution. Merely by way of example, the instructions may initiallybe carried on a magnetic disk and/or optical disc of a remote computer.A remote computer might load the instructions into its dynamic memoryand send the instructions as signals over a transmission medium to bereceived and/or executed by computer system 1500.

The communications subsystem 1519 and/or components thereof generallywill receive signals, and the bus 1505 then might carry the signalsand/or the data, instructions, etc. carried by the signals to theworking memory 1535, from which the processor(s) 1510 retrieves andexecutes the instructions. The instructions received by the workingmemory 1535 may optionally be stored on a non-transitory storage device1525 either before or after execution by the processor(s) 1510.

The methods, systems, and devices discussed above are examples. Variousconfigurations may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods may be performed in an order different from that described,and/or various stages may be added, omitted, and/or combined. Also,features described with respect to certain configurations may becombined in various other configurations. Different aspects and elementsof the configurations may be combined in a similar manner. Also,technology evolves and, thus, many of the elements are examples and donot limit the scope of the disclosure or claims.

Specific details are given in the description to provide a thoroughunderstanding of exemplary configurations including implementations.However, configurations may be practiced without these specific details.For example, well-known circuits, processes, algorithms, structures, andtechniques have been shown without unnecessary detail in order to avoidobscuring the configurations. This description provides exampleconfigurations only, and does not limit the scope, applicability, orconfigurations of the claims. Rather, the preceding description of theconfigurations will provide those skilled in the art with an enablingdescription for implementing described techniques. Various changes maybe made in the function and arrangement of elements without departingfrom the spirit or scope of the disclosure.

Also, configurations may be described as a process which is depicted asa schematic flowchart or block diagram. Although each may describe theoperations as a sequential process, many of the operations can beperformed in parallel or concurrently. In addition, the order of theoperations may be rearranged. A process may have additional steps notincluded in the figure. Furthermore, examples of the methods may beimplemented by hardware, software, firmware, middleware, microcode,hardware description languages, or any combination thereof. Whenimplemented in software, firmware, middleware, or microcode, the programcode or code segments to perform the necessary tasks may be stored in anon-transitory computer-readable medium such as a storage medium.Processors may perform the described tasks.

Having described several example configurations, various modifications,alternative constructions, and equivalents may be used without departingfrom the spirit of the disclosure. For example, the above elements maybe components of a larger system, wherein other rules may takeprecedence over or otherwise modify the application of the technology.Also, a number of steps may be undertaken before, during, or after theabove elements are considered. Accordingly, the above description doesnot bind the scope of the claims.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural references unless the context clearly dictatesotherwise. Thus, for example, reference to “a user” includes a pluralityof such users, and reference to “the processor” includes reference toone or more processors and equivalents thereof known to those skilled inthe art, and so forth.

Also, the words “comprise”, “comprising”, “contains”, “containing”,“include”, “including”, and “includes”, when used in this specificationand in the following claims, are intended to specify the presence ofstated features, integers, components, or steps, but they do notpreclude the presence or addition of one or more other features,integers, components, steps, acts, or groups.

It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this applicationand scope of the appended claims.

What is claimed is:
 1. A method of operating an optical system, themethod comprising: defining, based on a vergence-accommodation conflict(VAC) limit, a delimited zone as a function of distance from the opticalsystem, the delimited zone having at least one distance threshold;determining a virtual distance of a virtual depth plane from the opticalsystem at which a virtual object is to be displayed; determining whetherthe virtual distance is outside the delimited zone by comparing thevirtual distance to the at least one distance threshold; generating, bya projector of the optical system, a collimated pixel beam associatedwith the virtual object; based on determining that the virtual distanceis outside the delimited zone, modifying the collimated pixel beam togenerate a modified pixel beam, wherein modifying the collimated pixelbeam includes at least one of: converging the collimated pixel beam; orreducing a diameter of the collimated pixel beam; injecting the modifiedpixel beam into an eyepiece of the optical system; and outputting themodified pixel beam from the eyepiece toward an eye of a user.
 2. Anoptical system comprising: a projector configured to generate acollimated pixel beam associated with a virtual object; a lightmodifying device configured to modify the collimated pixel beam togenerate a modified pixel beam; an eyepiece configured to output themodified pixel beam; and a processing module configured to performoperations comprising: determining a virtual distance of a virtual depthplane from the optical system at which the virtual object is to bedisplayed; comparing the virtual distance to at least one distancethreshold; and based on comparing the virtual distance to the at leastone distance threshold, causing the light modifying device to modify thecollimated pixel beam to generate the modified pixel beam.
 3. Theoptical system of claim 2, wherein modifying the collimated pixel beamincludes: converging the collimated pixel beam.
 4. The optical system ofclaim 2, wherein modifying the collimated pixel beam includes: reducinga diameter of the collimated pixel beam.
 5. The optical system of claim2, wherein the operations further comprise: defining a delimited zone asa function of distance from the optical system, the delimited zoneincluding the at least one distance threshold.
 6. The optical system ofclaim 5, wherein comparing the virtual distance to the at least onedistance threshold includes: determining whether the virtual distance isoutside the delimited zone.
 7. The optical system of claim 5, whereinthe delimited zone is defined based on a vergence-accommodation conflict(VAC) limit.
 8. The optical system of claim 7, wherein the VAC limit isdefined by a user of the optical system.
 9. The optical system of claim2, wherein the eyepiece is configured to receive the modified pixel beamfrom the light modifying device.
 10. The optical system of claim 2,wherein the light modifying device is positioned in an optical pathbetween the projector and the eyepiece.
 11. A method of operating anoptical system, the method comprising: determining a virtual distance ofa virtual depth plane from the optical system at which a virtual objectis to be displayed; comparing the virtual distance to at least onedistance threshold; generating, by a projector of the optical system, acollimated pixel beam associated with the virtual object; and based oncomparing the virtual distance to the at least one distance threshold,modifying the collimated pixel beam to generate a modified pixel beam.12. The method of claim 11, wherein modifying the collimated pixel beamincludes: converging the collimated pixel beam.
 13. The method of claim11, wherein modifying the collimated pixel beam includes: reducing adiameter of the collimated pixel beam.
 14. The method of claim 11,further comprising: defining a delimited zone as a function of distancefrom the optical system, the delimited zone including the at least onedistance threshold.
 15. The method of claim 14, wherein comparing thevirtual distance to the at least one distance threshold includes:determining whether the virtual distance is outside the delimited zone.16. The method of claim 14, wherein the delimited zone is defined basedon a vergence-accommodation conflict (VAC) limit.
 17. The method ofclaim 16, wherein the VAC limit is defined by a user of the opticalsystem.
 18. The method of claim 11, further comprising: injecting themodified pixel beam into an eyepiece of the optical system.
 19. Themethod of claim 11, further comprising: outputting the modified pixelbeam from an eyepiece of the optical system toward an eye of a user. 20.The method of claim 11, wherein the collimated pixel beam is modified bya light modifying device positioned in an optical path between theprojector and an eyepiece of the optical system.